People say they were born this way when they really mean that they don't feel like it's a choice. As far as I understand it, it's a mixture of nature and nurture, so both genes and the environment shape someone's sexuality. That doesn't mean that we have a choice in our sexuality, that we know what in our environment affects us in what way, that the same things in our environment affect different people's sexuality the same way, nor that there is any way far us to prevent or change it. What's clear is that there is a significant genetic component, that the vast (very vast) majority of us gay people don't think that we had any choice in our sexuality (just think of of how your sexuality developed and whether you folt you had any choice), but that genes don't fully determine (at least not in all cases) the person's sexuality.